# project

`project(cmd0::String="", arg1=nothing, kwargs...)`

*keywords: GMT, Julia, great circles*

Project data onto lines or great circles, or generate tracks

## Description

Reads arbitrary (\(x\), \(y\) [,\*z*]) data and writes any combination of (\(x, y\), *z*, \(p, q, r, s\)), where (\(p, q\)) are the coordinates in the projection, (\(r, s\)) is the position in the (\(x, y\)) coordinate system of the point on the profile (\(q = 0\) path) closest to (\(x, y\)), and *z* is all remaining columns in the input (beyond the required \(x\) and \(y\) columns).

Alternatively, **project** may be used to generate (\(r,s,p\)) triples at equal increments *dist* along a profile using **step**. In this case, no input is read.

Projections are defined in one of three ways:

By a center (

*cx,cy*) using**origin**and an azimuth in degrees clockwise from North using**azim**.By a center (

*cx,cy*) using**origin**and end point (*bx,by*) of the projection path using**endpoint**.By a center (

*cx,cy*) using**origin**and a rotation pole position (*px,py*) using**pole**(not allowed when a Cartesian transformation is set by**flat_earth**).

To spherically project data along a great circle path, an oblique coordinate system is created which has its equator along that path, and the zero meridian through (*cx,cy*). Then the oblique longitude (\(p\)) corresponds to the distance from (*cx,cy*) along the great circle, and the oblique latitude (*q*) corresponds to the distance perpendicular to the great circle path. When moving in the increasing (\(p\)) direction, (in the direction set by **azim** *azimuth* ), the positive (\(q\)) direction is to the left. If a pole has been specified by **pole**, then the positive (*q*) direction is toward the pole.

To specify an oblique projection, use the **pole** option to set the pole. Then the equator of the projection is already determined and the **origin** option is used to locate the \(p = 0\) meridian. The center *(cx,cy)* will be taken as a point through which the \(p = 0\) meridian passes. If you do not care to choose a particular point, use the South pole (*cx* = 0, *cy* = -90).

Data can be selectively windowed by using the **length** and **width** options. If **width** is used, the projection width is set to use only points with \(w_{min} < q < w_{max}\). If **length** is set, then the length is set to use only those points with \(l_{min} < p < l_{max}\). If the **endpoint** option has been used to define the projection, then **length**\**w** may be selected to window the length of the projection to exactly the span from the center (**origin**) to to the endpoint (**endpoint**).

Flat Earth (Cartesian) coordinate transformations can also be made. Set **flat_earth** and remember that *azimuth* is clockwise from North (the \(y\) axis), NOT the usual cartesian theta, which is counterclockwise from the \(x\) axis. (i.e., \(azimuth = 90 - theta\)).

No assumptions are made regarding the units for \(x, y, r, s, p, q\), *dist*, \(l_{min}, l_{max}, w_{min}, w_{max}\). However, if **km** is selected, map units are assumed and \(x, y, r, s\), must be in degrees and \(p, q\), *dist*, \(l_{min}, l_{max}, w_{min}, w_{max}\) will be in km.

Calculations of specific great-circle and geodesic distances or for back-azimuths or azimuths are better done using mapproject as **project** is strictly spherical.

```
using GMT
a = atand(4 / 2.5)
X = project([0 0], origin=(0,-1), endpoint=(2.5,3), flat_earth=true)
plot([-1.5 -1.0625; 0 -2; 2 1.2; 0.5 2.1375], region=(-3.5,4,-2.7,2.6), fill=:lightgray,
xlabel="@%7%x@%% or @%7%r@%%", ylabel="@%7%y@%% or @%7%s@%%", figsize="12/0")
plot!([0 -1; 2 2.2], marker=:circ, ms=0.3, fill=:orange, frame=(grid=10,))
arrows!([0 -1 2 2.2; 0 -1 -2.5 0.5625], arrow=(len="16p", stop=true, shape=1),
endpoint=true, lw=2, fill=:black)
plot!([0 0], marker=:circ, ms=0.3, fill=:red)
# Get coordinates of the (0,q) point as well so we can dash the line
x = -X[4] * sind(a)
y = X[4] * cosd(a) - 1
plot!([X[5] X[6]], marker=:circ, ms=0.2, fill=:blue)
T = mat2ds([ 0 -1 0;
2 2.2 0;
1.9 1.9 a;
-2.3 0.4 a;
2 1.2 a;
0 -2 a;
0 -2 a;
-1.5 -1.0625 a;
0.45 0.8 -16],
["TL @%7%C@%%", "BR @%7%E@%%", "TC p", "RM q", "TC L@-max@-",
"TC L@-min@-", "RB W@-min@-", "RM W@-max@-", "TC @~a@~"])
text!(T, font=(12, "Times-Italic"), angle="", justify="", offset=(away=true, shift=0.15))
plot!([0 0; X[5] X[6]], pen=(0.25, :red, :dash))
plot!([0 0; x y], pen=(0.25, :red, :dash))
plot!([0.0 -1], marker=(:matangle, [2.54 a 90], (length="9p", start=true)), ml=0.5, fill=:black)
showfig()
```

Explanation of the coordinate system utilized by project. The input point (red circle) is given in the original *x-y* (or *lon-lat*) coordinate system and is projected to the *p-q* coordinate system, defined by the center (**center**) and either the end-point (**outvars**) or azimuth (\(\alpha\)), or for geographic data a rotation pole **pole** (not shown). The blue point has projected coordinates (p,0) and is reported as (r,s) in the original coordinate system. Options **length** (limit range of *p*) and **width** (limit range of *q*) can be used to exclude data outside the specified limits (light gray area).

## Required Arguments

*table*

One or more data tables holding a number of data columns.

**C**or**origin**or**start_point**: –*origin=(cx, cy)*

Set the origin*cx,cy*of the projection when used with**azim**or**endpoint**or set the coordinates*cx,cy*of a point through which the oblique zero meridian (\(p = 0\)) should pass when used with**pole**.*cx,cy*is not required to be 90 degrees from the pole set by**pole**.

## Optional Arguments

**A**or**azim**or**azimuth**: –*azim=az*

Set the*azimuth*of the projection. The*azimuth*is clockwise from North (the \(y\) axis) regardless of whether spherical or Cartesian coordinate transformation is applied.

**E**or**endpoint**or**end_pt**: –*endpoint=(bx,by)*

Set the end point*bx,by*of the projection path.

**F**or**outvars**: –*outvars=flags*

Specify the desired output using any combination of*xyzpqrs*in any order, where (\(p, q\)) are the coordinates in the projection, (\(r, s\)) is the position in the (\(x, y\)) coordinate system of the point on the profile (\(q = 0\) path) closest to (\(x, y\)), and*z*is all remaining columns in the input (beyond the required \(x\) and \(y\) columns). [Default is*xyzpqrs*]. If output format is ASCII then*z*also includes any trailing text (which is placed at the end of the record regardless of the order of*z*in*flags*). Use lower case and do not add spaces between the letters.**Note**: If**step**is selected, then the output order is set to be*rsp*and**outvars**is not allowed.

**G**or**step**or**generate**: –*step="dist[*unit*][/*colat*][***+c**][**+h**][**+n**]"

Create (*r*,*s*,*p*) output points every*dist*units of*p*, assuming all units are the same unless \(x, y, r, s\) are set to degrees using**km**. No input is read when**step**is used. See`Units`

for selecting geographic distance units [km]. The following directives and modifiers are supported:

- Optionally, append /*colat* for a small circle instead [Default is a colatitude of 90, i.e., a great circle]. Note, when using **origin** and **endpoint** to generate a circle that goes through the center and end point, the center and end point cannot be farther apart than \(2|colat|\). - Optionally, append **+c** when using **pole** to calculate the colatitude that will lead to the small circle going through the center *cx*/*cy*. - Optionally, append **+h** to report the position of the pole as part of the segment header when using **pole** [Default is no header]. - Optionally, append **+n** to indicate a desired number of points rather than an increment. Requires **origin** and **endpoint** or |-Z| so that a length can be computed.

**L**or**length**: –*length=(lmin,lmax)***|***length=:w*

Specify length controls for the projected points. Project only those points whose*p*coordinate is within \(l_{min} < p < l_{max}\). If**endpoint**has been set, then you may alternatively use**length=:w**to stay within the distance from*cx,cy*to*bx,by*.

**N**or**flat_earth**: –*flat_earth=true*

Specify the Flat Earth case (i.e., Cartesian coordinate transformation in the plane). [Default uses spherical trigonometry.]

**Q**or**km**: –*km=true*

Specify that*x*,*y*,*r*,*s*are in degrees while*p*,*q*,*dist*,*lmin*,*lmax*,*wmin*,*wmax*are in km. If**km**is not set, then all these are assumed to be in the same units.

**S**or**sort**: –*sort=true*

Sort the output into increasing*p*order. Useful when projecting random data into a sequential profile.

**T**or**pole**: –*pole=(px,py)*

Set the position of the rotation pole of the projection as*px,py*.

**V**or*verbose*: –*verbose=true***|***verbose=level*

Select verbosity level. More at verbose

**W**or**width**: –*width=(wmin,wmax)*

Specify width controls for the projected points. Project only those points whose*q*coordinate is within \(w_{min} < q < w_{max}\).

**Z**or**ellipse**: –*ellipse="major[*unit*][/*minor*/*azimuth*][***+e**]"

Create the coordinates of an ellipse with*major*and*minor*axes given in km (unless**flat_earth**is given for a Cartesian ellipse) and the*azimuth*of the major axis in degrees; used in conjunction with**origin**(sets its center) and**step**(sets the distance increment).**Note**: For the Cartesian ellipse (which requires**flat_earth**), we expect*direction*counter-clockwise from the horizontal instead of an*azimuth*. A geographic*major*may be specified in any desired unit [Default is km] by appending the unit (e.g., 3d for degrees); if so we assume the*minor*axis and the increment are also given in the same unit (see`Units`

). For degenerate ellipses you can just supply a single*diameter*instead. The following modifiers are supported:

- Append **+e** to adjust the increment set via **step** so that the ellipse has equal distance increments [Default uses the given increment and closes the ellipse].

**bi**or**binary_in**: –*binary_in=??*

Select native binary format for primary table input. More at

**bo**or**binary_out**: –*binary_out=??*

Select native binary format for table output. More at

**di**or**nodata_in**: –*nodata_in=??*

Substitute specific values with NaN. More at

**e**or**pattern**: –*pattern=??*

Only accept ASCII data records that contain the specified pattern. More at

**f**or**colinfo**: –*colinfo=??*

Specify the data types of input and/or output columns (time or geographical data). More at

**g**or**gap**: –*gap=??*

Examine the spacing between consecutive data points in order to impose breaks in the line. More at

**h**or**header**: –*header=??*

Specify that input and/or output file(s) have n header records. More at

**i**or**incol**or**incols**: –*incol=col_num***|***incol="opts"*

Select input columns and transformations (0 is first column, t is trailing text, append word to read one word only). More at incol

**o**or**outcol**: –*outcol=??*

Select specific data columns for primary output, in arbitrary order. More at

**q**or**inrows**: –*inrows=??*

Select specific data rows to be read and/or written. More at

**s**or**skiprows**or**skip_NaN**: –*skip_NaN=true***|***skip_NaN="<cols[+a][+r]>"*

Suppress output of data records whose z-value(s) equal NaN. More at

**yx**: –*yx=true*

Swap 1st and 2nd column on input and/or output. More at

**Units**

For map distance unit, append unit d for arc degree, m for arc minute, and s for arc second, or e for meter [Default unless stated otherwise], f for foot, k for km, M for statute mile, n for nautical mile, and u for US survey foot. By default we compute such distances using a spherical approximation with great circles (-jg) using the authalic radius (see `PROJ_MEAN_RADIUS`

). You can use -jf to perform “Flat Earth” calculations (quicker but less accurate) or -je to perform exact geodesic calculations (slower but more accurate; see `PROJ_GEODESIC`

for method used).

## Examples

To project the remote data sets ship_03.txt (lon,lat,depth) onto a great circle specified by the two points (330,-18) and (53,21) and sort the records on the projected distances along that circle and only output the distance and the depths, try

```
using GMT
D = project("@ship_03.txt", origin=(330,-18), pole=(53,21), sort=true, outvars=:pz, km=true)
imshow(D)
```

To generate points every 10 km along a great circle from 10N,50W to 30N,10W:

```
using GMT
Dgc = project(origin=(-50,10), endpoint=(-10,30), step=10, km=true)
imshow(Dgc, marker=:point, lw=0.5, coast=true)
```

(Note that `Dgc`

could now be used as input for grdtrack, etc. ).

To generate points every 1 degree along a great circle from 30N,10W with azimuth 30 and covering a full 360, try:

```
D = project(origin=("10W","30N"), azim=30, step=1, length=(-180,180))
imshow(D, coast=true)
```

To generate points every 10 km along a small circle of colatitude 60 from 10N,50W to 30N,10W:

```
using GMT
Dsc = project(origin=(-50,10), endpoint=(-10,30), step=(10,60), km=true)
imshow(Dsc, marker=:point, lw=0.5, coast=true)
```

To create a partial small circle of colatitude 80 about a pole at 40E,85N, with extent of 45 degrees to either side of the meridian defined by the great circle from the pole to a point 15E,15N, try

`D = project(origin=(15,15), pole=(40,85), step=(1,80), length(-45,45))`

To generate points approximately every 10 km along an ellipse centered on (30W,70N) with major axis of 1500 km with azimuth of 30 degree and a minor axis of 600 km, try

```
using GMT
Dellip = project(origin=(-30,70), step=10, ellipse="1500/600/30+e", km=true)
imshow(Dellip, coast=true)
```

To project the shiptrack gravity, magnetics, and bathymetry in c2610.xygmb along a great circle through an origin at 30S, 30W, the great circle having an azimuth of N20W at the origin, keeping only the data from NE of the profile and within ± 500 km of the origin, run:

```
Dprj = project("c2610.xygmb", origin=(-30,-30), azim=-20, width=(-10000,0),
length=(-500,500), outvars=:pz, km=true)
```

(Note in this example that **width=(-10000,0)** is used to admit any value with a large negative *q* coordinate. This will take those points which are on our right as we walk along the great circle path, or to the NE in this example.)

To make a Cartesian coordinate transformation of mydata.xy so that the new origin is at 5,3 and the new *x* axis (*p*) makes an angle of 20 degrees with the old *x* axis, use:

`D = project("mydata.xy", origin=(5,3), azimuth=70, outvars=:pq)`

To take data in the file pacific.lonlat and transform it into oblique coordinates using a pole from the hotspot reference frame and placing the oblique zero meridian (*p* = 0 line) through Tahiti, run:

`D = project("pacific.lonlat", pole=(-75,68), origin=("-149:26","-17:37"), outvars=:pq)`

Suppose that pacific_topo.nc is a grid file of bathymetry, and you want to make a file of flowlines in the hotspot reference frame. If you run:

```
G = grd2xyz("pacific_topo.nc");
D = project(pole=(-75,68), oigin=(0,-90), outvars=:xyq);
Gflow = xyz2grd(region=etc, inc=etc);
```

then `Gflow`

is a grid in the same area as pacific_topo.nc, but flow contains the latitudes about the pole of the projection. You now can use grdcontour on `Gflow`

to draw lines of constant oblique latitude, which are flow lines in the hotspot frame.

If you have an arbitrarily rotation pole *px,py* and you would like to draw an oblique small circle on a map, you will first need to make a file with the oblique coordinates for the small circle (i.e., lon = 0-360, lat is constant), then create a file with two records: the north pole (0/90) and the origin (0/0), and find what their oblique coordinates are using your rotation pole. Now, use the projected North pole and origin coordinates as the rotation pole and center, respectively, and project your file as in the pacific example above. This gives coordinates for an oblique small circle.

## See Also

fitcircle, gmtvector, grdtrack, mapproject, grdproject, grdtrack

These docs were autogenerated using GMT: v1.11.0